This invention relates to a valve operating mechanism for internal combustion engines and more particularly to an apparatus for varying the valve lift and timing in accordance with the varying operating conditions of the engine.
The customary internal combustion engine utilizes a valve operating mechanism constructed to control the opening and closing of the intake and exhaust valves at timings which are fixed for all operating conditions of the engine in a manner to meet the requirement of the high-speed operating conditions of the engine. Such a valve operating mechanism, however, causes incomplete combustion of the mixture during idling and at low engine speeds due to excessively large valve overlap at such engine speeds, resulting in high pollution levels from the engine, marked deterioration of fuel economy and a loss in engine performance efficiency during idling and at low engine speeds.
With a view to eliminating these problems in such a valve operating mechanism, various valve operating mechanisms have heretofore been proposed which are operative to vary valve lift and timing, but difficulties are still encountered in such variable valve operating mechanisms' being put to practical use due to their relatively complex and bulky construction and due to the difficulty in controlling the valve timing strictly in accordance with the varying operating conditions of the engine. For example, a variable valve timing camshaft is known which has a relatively good practical usefulness but has difficulty in controlling the valve timing strictly in accordance with the varying operating conditions of the engine. Furthermore, the customary variable valve timing camshaft cannot vary the valve lift profile and the valve opening period. The present invention is directed to elimination of all these problems inherent in the prior art valve operating mechanisms of the type providing variable valve timing as well as of the type providing constant valve lift and timing.